Feature: Add support for custom GraphQL scalars @gql(scalars: { website: "AWSURL" })

[Tenrys]

Right now it seems like only fields that are named url or email have been hardcoded to use the AWSURL and AWSEmail scalar types from AWS, however I would like to be able to use these types on fields like urlPhoto or something like secondaryEmail.

As seen here:

prisma-appsync/packages/generator/src/compiler.ts

Lines 859 to 868 in 37b4a68

	if (type === 'String') {
	switch (field.name.toLocaleLowerCase()) {
	case 'email':
	type = 'AWSEmail'
	break
	case 'url':
	type = 'AWSURL'
	break
	}
	}

Would it be possible to use triple slash comments in the Prisma schema to define which fields turn up as what scalar types in the GraphQL schema?

[maoosi]

Possibly yes, but would need to find the right syntax...

There is already a custom notation in place (not documented yet) that allows customising the generated GraphQL schema.

/// @gql(queries: { list: null, count: "countyPosts" }, fields: { text: null }, subscriptions: null)
model Post {
    text  String?
    urlPhoto  String?
}

The above notation equals to:

• Remove listPosts
• Rename countPosts to countyPosts
• Remove text field
• Remove all subscriptions

One option could be:

/// @gql(scalars: { urlPhoto: "AWSURL" })
model Post {
    urlPhoto  String?
}

Implementing the above would be quite simple, as the code to read the @gql directive is already in place.

What do you think?

[Tenrys]

I think that makes sense yes! Until documentation gets written, is there a way to know where exactly the code involving that custom notation is in place?

[maoosi]

Parsing the @gql directive as a JSON object is done here:

prisma-appsync/packages/generator/src/compiler.ts

Lines 367 to 375 in 37b4a68

	const gqlDirectives = directives.match(gqlRegex)
	if (gqlDirectives) {
	for (let i = 0; i < gqlDirectives.length; i++) {
	const str = replaceAll(gqlDirectives[i].replace(gqlRegex, '$1'), find, replace)
	// eslint-disable-next-line no-new-func
	gql = merge({}, gql, new Function(`return ({${str}})`)())
	}
	}

The following is the config object where to add _scalars: gqlObject?.scalars || {}:

prisma-appsync/packages/generator/src/compiler.ts

Lines 393 to 406 in 37b4a68

	const gqlOutput: {
	_model: boolean
	_fields: any
	_usesQueries: boolean
	_usesMutations: boolean
	_usesSubscriptions: boolean
	[key: string]: any
	} = {
	_model: gqlObject?.model !== null,
	_fields: gqlObject?.fields || {},
	_usesQueries: false,
	_usesMutations: false,
	_usesSubscriptions: false,
	}

Here is where the check to ignore fields is done:

prisma-appsync/packages/generator/src/compiler.ts

Lines 544 to 567 in 37b4a68

	const isFieldIgnored = gqlConfig?._fields?.[field.name] === null
	if (!field.isGenerated && !isFieldIgnored) {
	fields.push({
	name: field.name,
	type: field.type,
	scalar: this.getFieldScalar(field),
	isRequired: this.isFieldRequired(field),
	isList: this.isFieldList(field),
	isEnum: this.isFieldEnum(field),
	isEditable: !this.isFieldGeneratedRelation(field, model),
	isUnique: this.isFieldUnique(field),
	...(field.relationName && {
	relation: {
	name: this.getFieldRelationName(field, model),
	kind: this.getFieldRelationKind(field),
	type: this.getFieldScalar(field),
	},
	}),
	directives,
	sample: this.getFieldSample(field),
	})
	}
	})

For example, we could do:

const scalar = gqlConfig?._scalars?.[field.name] || this.getFieldScalar(field)

[maoosi]

@Tenrys do you want to work on a PR for this feature?

[maoosi]

Will be released as part of 1.0.0-rc.6 (you can also try it now with prisma-appsync@1.0.0-preview.6.6).